Micromachining technology has been developed to fabricate microstructure devices which are recently applied in various fields. The micromachining technology is referred to as micro electro mechanical systems technology (MEMS technology) and the microstructure devices also referred to as MEMS devices.
A mobile communication device such as a mobile phone is an example of the fields as the application of the MEMS technology. MEMS technology makes MEMS devices such as variable capacitors and switches as radio frequency devices (RF devices) suitable to be used in radio-frequency circuits in the mobile phone, for example.
The variable capacitors and the switches in MEMS devices, often need a beam structure which gives a function permitting vertical movement on a substrate on which the MEMS device is formed.
The beam structures having the above-mentioned function are described in Japanese Laid-open Patent Publications No. 2005-313276 and No. 2006-289520. There is described in the former Patent Publication that the MEMES device has a piezoelectric film disposed over a cavity formed in a substrate, a movable beam having a first electrode disposed at the central part of the piezoelectric film, and a second electrode disposed in the cavity so as to face the first electrode.
There is described in the latter patent application that MEMS device has a lower electrode disposed at the bottom of a cavity, an actuator disposed over or inside the cavity, and an upper electrode connected to the actuator.